1. Field of the Invention
Present invention relates to an electrode-built-in susceptor. In particular, the present invention relates to an electrode-built-in susceptor which can prevent a leak electricity under s high temperature oxidizing atmosphere condition.
2. Description of Related Art
In recent years, manufacturing processes such as an etching process, a coating process are performed per a wafer or per a base board uniformly in a production process for a semiconductor device such as an IC (integrated circuit), an LSI (large scale integration), VLSI (very large scale integration). It is the same for manufacturing process for a display device such as a liquid crystal display (LCD) and a plasma display (PDP) and an assembly process for a hybrid IC of the like. A sheet-by-sheet process for a plate sample such as a semiconductor device, a glass base board for a liquid crystal, and a printed circuit board is becoming more common.
In such a sheet-by-sheet process, a plate sample is supported in a processing chamber sheet by sheet, or wafer by wafer. The plate sample is mounted on a sample base which is called as a susceptor and processed for a predetermined time.
It is necessary that such a susceptor can be used under a high temperature plasma condition. Therefore, it is required that such a susceptor has a superior plasma characteristics and a larger thermal conductivity.
For such a susceptor, a susceptor which is made of a aluminium-nitride-group-sintered-member having superior high temperature anti-plasma characteristics is commonly used.
There is a case in which an electrostatic chucking electrode for fixing a plate sample by generating an electric charge and an electrostatic absorbing force is disposed in the susceptor. Also, there is a case in which a heating electrode for heating the plate sample by an electricity is disposed in the susceptor. Also, there is a case in which an inner electrode for generating a plasma by applying a high frequency electricity is disposed in the susceptor.
FIG. 6 is a cross section showing an example for such an electrode-built-in susceptor. Here, an electrode-built-in susceptor 1 comprises a mounting plate 2 which is formed by an aluminium-nitride-group-sintered-member of which upper surface is a mounting surface 2a for mounting a plate sample (not shown in the drawing) thereon, a supporting plate 3 which is formed by an aluminium-nitride-group-sintered-member for supporting the mounting plate 2 from therebeneath, a plurality of inner electrodes 4 which are supported between the mounting plate 2 and the supporting plate 3, and power supplying terminals 6, 6 which are disposed in a fixing holes 5 formed in the supporting plate 3 so as to contact the inner electrodes 4. These power supplying terminals 6, 6 are formed by a heat-resistance metal such as a molybdenum (Mo) and a tungsten (W).
In such an electrode-built-in susceptor 1, the mounting plate 2 and the supporting plate 3 for supporting the inner electrodes 4 are formed by an aluminium-nitride-group-sintered-member; therefore, such an electrode-built-in susceptor is used preferably in a plasma-etching-apparatus or a plasma CVD (chemical vapor disposition) apparatus in which an anti-plasma characteristics and a thermal conductivity are necessary particularly.
Here, the aluminum-nitride-group-sintered-member which forms the above mounting plate 2 and the supporting plate 3 is very insulating under an ordinary temperature condition. However, the insulating characteristics in the aluminum-nitride-group-sintered-member tends to worsen under a high temperature oxidizing condition such as 400° C. or higher. A resistance value in the mounting plate 2 and the supporting plate 3 become worsened if such an electrode-built-in susceptor 1 is used under a high temperature atmosphere condition; thus, a leak electricity may easily occurs when an electricity is charged to the inner electrodes 4. As a result, there are problems in that the leak electricity damages a plate sample which is mounted on the mounting surface, or it is not possible to control an electric conductivity to the inner electrodes 4 because of such a leak electricity.
Correspondingly, it is proposed recently to use an aluminium-nitride-group-sintered-member to which a magnesium compound such as a magnesium oxide (MgO) is doped so as to alleviate a temperature dependency of an initial volume resistance value in the aluminium-nitride-group-sintered-member. There is a problem in that a thermal efficiency is reduced because of a reduced thermal conductivity of the aluminium-nitride-group-sintered-member in such an electrode-built-in susceptor. In addition, there is a new problem in that a magnesium which is contained in the aluminium-nitride-group-sintered-member may be a contamination source for the plate sample.
On the other hand, it is necessary to apply a 20 A electricity when, for example, the inner electrodes 4 are used for a plasma generating electrodes under condition a large amount of electricity is applied to the inner electrodes 4 in the power supplying terminals 6, 6. Therefore, it is necessary to reduce the resistance value in the power supplying terminals 6, 6. As a result, it is necessary to increase a diameter of the power supplying terminal 6. Therefore, a stress becomes large which is caused by a difference between a thermal expansion in a heat-resistance metal which forms the power supplying terminals 6, 6 and a thermal expansion in the aluminium-nitride-group-sintered-member which forms the supporting plate 3. Thus, there is a problem in that a crack may occur easily on the supporting plate 3 according to a thermal condition change when such an electrode-built-in susceptor is used.
Here, recently, it is tentatively proposed to form power supplying terminals 6, 6 by a conductive sintered member such as an aluminium-nitride-tungsten-composite-sintered-member. However, such a sintered member does not have sufficient anti-oxidization characteristics. For example, there is a problem in that such a sintered member does not have a durability to a thermal cyclic load in which a heating operation and a cooling operation are repeated under 400° C. temperature oxidizing atmosphere condition.
In order to solve such a problem, it is proposed to cool the power supplying terminals 6, 6 by a cooling section. In such a case, another problem arises in that it takes more time to heat the plate sample at a predetermined temperature and the heat does not distribute in the plate sample uniformly.